The absorbent core of infant diapers, incontinence and feminine hygiene products is today covered by at least two layers on the side worn next to the body. Between the cover non-woven fabric or the perforated film and the absorbent core is positioned an acquisition and distribution layer (ADL) of non-woven fabric or reticulated foam, which as the name implies, quickly takes up the body fluid (urine, thin feces or menses) and distributes it as uniformly as possible to the absorbent core lying under it, which is normally made of cellulose and super absorbent powder. This keeps the human skin dry, thus preventing skin irritation as well as leakage of the body fluid at the sides. The back of the absorbent hygiene product is sealed against permeation of body fluid by a watertight film or a non-woven-film laminate.
Non-woven fabrics bonded thermally in a hot air dryer or non-woven fabrics of crimped, relatively coarse denier fibers bonded by polymer dispersions are known for use in ADLs. The fibers have deniers greater than 3.3 dtex and are made up primarily of polyester (polyethylene terephthalate) and/or polyolefins, bicomponent fibers having a side-by-side or a core/jacket structure being used for fiber bonding in the through-flow oven and one of the two fiber components being melted significantly more deeply than the other component. In relation to their low weight, such non-woven fabrics have a relatively high bulk (thickness). It is known, however, that this initial thickness is already significantly reduced when the product is rolled up under stresses ordinarily used and the pressure conditions in the packaging contribute further to the reduction in thickness.
For that reason, means have been sought to achieve a thickness not only by using crimped fibers having a more or less statistical distribution and their bonding but also to bring such crimped non-woven fabrics into the third dimension, which we will consistently describe as the Z-direction in the following, by undulation or other geometric orientations. It has been shown that this makes it possible to attain higher compression resistances than by using high-loft non-woven fabrics with the consequence of significantly reduced loss of thickness when a diaper passes through the production steps, including packaging and storage.
An embossing method for manufacturing a structured, bulky non-woven fabric is described in DE 197 25 749 A1. A pre-bonded spun non-woven fabric, the endless filaments of which have been drawn to only 50% to 70% of the maximum possible draw ratio, are subjected to a particular finishing treatment. In doing so, the spun non-woven fabric is passed between a positive roller having a knobby surface and a negative roller having lamellar strips positioned transverse to the machine direction, the strips meshing with the channels kept open by the knobs. This results in 3D non-woven fabrics having areas of conically shaped weight-thinned elevations that are surrounded by linear, undeformed areas.
The disadvantage of the embossing method described in DE 197 25 749 A1 is that it is limited to undrawn or partially drawn endless filament non-woven fabrics (spun non-woven fabrics). Such non-woven fabrics are made from coarse-denier, uncrimped endless fibers that are known to result in hard, rough and non-textile products and therefore are not used as ADLs in diapers. Such endless filaments having a side-by-side structure or an asymmetric core/jacket structure do not result in crimping in a partially drawn state. Such crimping is ordinarily triggered by subsequent thermal processing, which in turn—as is known to those skilled in the art—prevents drawability (or formability) due to the crystallization which has occurred. Consequently, the prerequisites for the applicability of the embossing method described in DE 197 25 749 A1 are lacking.
A fluid distribution material having improved fluid distribution properties is described in EP-B 0.809.991 and EP-A 0.810.078. In this case, a plastically deformable web is formed into a non-woven fabric having a 3D structure by passing it through a pair of negative/positive rollers. A variation of the two applications referenced above is the embossed material and method for it, which is described in EP-B 0.499.942. However, such structures similar to corrugated cardboard have the disadvantage that they do not withstand any sustained pressure loads.
In EP applications 1.047.824, 1.047.823, 1.047.822 and 1.047.821, non-woven fabrics having elevations and indentations are produced in an intermediate step by passing the sheet material over two heated toothed gear rollers. The ribbings have little compression stability based on the fact that they lack a non-stabilizing fabric, which is glued to one side of the elevations or stiffenings. In the patent applications cited, it is rather the case that the undulations must be removed to the greatest possible extent or partially removed to produce soft and slightly elastic products transverse to the undulation.
Absorbent disposable items having a fecal management layer are known from EP-A 0.976.375, EP-A 0.976.374 and EP-A 0.976.373, the latter being made from an undulated non-woven fabric to which a flat non-woven fabric backing (EP-A 0.976.375) is cemented. Thick polymer filaments (EP-A 0.976.374) or meshed fabrics (EP-A 0.976.37) may be used instead of the non-woven fabric backing. Such undulated non-woven fabric laminates stabilized by a backing have proven to be suitable ADLs for fecal management and improved urine management. However, the production of such 3D laminate structures is very elaborate and requires two components and an additional adhesive in many cases. However, the use of a thick monofilament (having a denier in the range of several thousand dtex) proved to be unsuitable because such monofilaments are undrawn (or come from a hole-type nozzle) and therefore stretch under the strong mechanical load in the machine direction in diaper production with thinning of the filament and thus have an unacceptable property in this respect.